PHB Page 211, Alter Self
You assume a different form. When you cast the spell, choose one of the following options, the effects of which last for the duration of the spell. While the spell lasts, you can end one option as an action to gain the benefits of a different one.
Change Appearance. You transform your appearance. You decide what you look like, including your height, weight, facial features, sound of your voice, hair length, coloration, and distinguishing characteristics, if any. You can make yourself appear as a member of another race, though none of your statistics change. You also can’t appear as a creature of a different size than you, and your basic shape stays the same; if you’re bipedal, you can’t use this spell to become quadrupedal, for instance. At any time for the duration of the spell, you can use your action to change your appearance in this way again.
PHB Page 233, Disguise Self
You make yourself—including your clothing, armor, weapons, and other belongings on your person—look different until the spell ends or until you use your action to dismiss it. You can seem 1 foot shorter or taller and can appear thin, fat, or in between. You can’t change your body type, so you must adopt a form that has the same basic arrangement of limbs. Otherwise, the extent of the illusion is up to you.
The changes wrought by this spell fail to hold up to physical inspection. For example, if you use this spell to add a hat to your outfit, objects pass through the hat, and anyone who touches it would feel nothing or would feel your head and hair. If you use this spell to appear thinner than you are, the hand of someone who reaches out to touch you would bump into you while it was seemingly still in mid-air.
To discern that you are disguised, a creature can use its action to inspect your appearance and must succeed on an Intelligence (Investigation) check against your spell save DC.
Can the 2nd-level Alter Self spell make the 1st-level Disguise Self spell obsolete, either by perfectly replicating the spell’s effects or by providing wholly superior effects? Based on past editions of D&D I would guess yes, but after reading the descriptions of the spells from the PHB I can’t quite tell.
Specifically, I’m asking this question because the Warlock gets two different invocations: one that allows at-will usage of Disguise Self (Mask of Many Faces), and one that allows at-will usage of Alter Self (Master of Myriad Forms). The Warlock can also trade old obsolete invocations for different ones during a level-up. Is it advantageous to trade the Disguise Self invocation for the Alter Self invocation? Is it optimal for a character specializing in Stealth/Disguise/Social abilities to have both?